The present invention relates to a focus position adjusting method and a focus position adjusting apparatus for use with an optical pickup provided in an information recording/reproducing apparatus such as a DVD player.
The present application claims priority from Japanese Application No. 2003-39653, the disclosure of which is incorporated herein by reference.
Conventionally, in a process for manufacturing a DVD player, the below-discussed well-known adjustment method is generally used to adjust the focus position of an optical pickup.
Namely, if the focus position of an optical pickup is deviated from an appropriate target position, an unfavorable effect will occur due to such a deviation (offset) from the target position. As a result, it is difficult to perform information recording/reproducing (in an appropriate focusing state) on an optical disc loaded in the DVD player. For this reason, in an actual manufacturing step before product shipment, test operation of each optical pickup is performed using a reflected light from an actual optical disc, thereby adjusting the focus position of each produced optical pickup.
In test operation, each optical pickup is rendered to perform usual recording/reproducing using an adjustment apparatus in which an optical disc has been loaded. In detail, a light beam is caused to irradiate the optical disc through an objective lens provided within the optical pickup, while a reflected light from the optical disc forms an incident light through the same objective lens.
Actually, an optical pickup contains not only an objective lens, but also a plurality of symmetrically divided light-receiving surfaces. In this way, it is possible to receive a reflected light transmitting through the objective lens on these divided light-receiving surfaces. An optical pickup further contains a light-receiving element for outputting photo-electric-conversion signal for generating RF signal or focus error signal, as well as a multi-lens located between the objective lens and the light-receiving element for correcting the focus of a reflected light with respect to the light-receiving element.
If the focus position of the reflected light in its optical axis direction is deviated from an appropriate target position, the focus position of the objective lens of the optical pickup will become inappropriate. In view of this, the multi-lens for correcting the focus of the reflected light is provided between the objective lens and the light-receiving element.
Here, in order to correct the focus of the reflected light transmitting through the objective lens, the position of the multi-lens in the direction of the optical axis is adjusted so that the reflected light is incident on the light-receiving surface arranged on the light-receiving element. Afterwards, the obtained photo-electric-conversion signal is used to adjust the focus position of the optical pickup to an appropriate target position.
However, in the above-described conventional focus position adjusting method, since an optical disc is loaded in each adjustment apparatus and the focus position of an optical pickup is adjusted in accordance with reproduced information signals, there has occurred a problem that adjustment result is likely to be affected by an optical disc manufacturing irregularity or the like.
Moreover, since an optical disc is apt to suffer from a distortion or warp, even if only one optical disc is used in the focus position adjustment, such an adjustment is likely to be carried out based on photo-electric-conversion signals affected by disc distortion, hence making it difficult to perform highly accurate focus position adjustment.
In addition, since optical discs have to be actually loaded into great number of adjustment apparatuses, an operation for adjusting the focus position of optical pickup will become too complicated and troublesome.